Split brushes



Dec. 22, 1959 P. E. LYDDON 2,918,591

SPLIT BRUSHES Filed May 14, 1956 5 Sheets-Sheet 1 Dec. 22, 1959 P. E. LYDDON 2,918,591

SPLIT BRUSHES Filed May 14, 1956 3 Sheets-Sheet 2 5W KW WM Dec. 22, 1959 P. E. LYDDON 2,918,591

SPLIT BRUSHES Filed May 14, 1956 3 Sheets-Slaeet 3 United States Patent O SPLIT BRUSHES Percy Edward Lyddon, Croydon, England, assignor to Morganite Incorporated, Long Island City, N.Y., a corporation of New York Application May 14, 1956, Serial No. 584,824

Claims priority, application Great Britain May 27, 1955 12 Claims. (Cl. 310-248) This invention comprises improvements in or relating to electric commutator or slip-ring split brushes of the type comprising two or more parts to bear on and sweep the surface of the commutator or slip-ring surface. In brushes of this type the parts are separate pieces capable of a certain degree of independent movement, especially tilting, in the brush box,and may be of the same or different thickness. The parts have usually some mechanical interlock or linkage but if this is not the case the split brush may be called a tandem brush, each part being pressed against the commutator or slip-ring surface by a separate spring linger. In any case the members are connected electrically to a common terminal.

It is known in such split brushes to control the distribution of the electrical loading of the brush as between its respective parts by making the parts of difierent composition or grain-structure or by taking the leads from the brush parts to respective electric current controlling means. One object of controlling the distribution of the electrical loading, i.e. the "irrent transmitted through the respective parts of the brush, has been to reduce the current density at the leaving edge of the brush. Further, a reason for making the brush in two or more separate parts has been to achieve division of the commutation voltage drop so that it is spread over two or more lines of contact instead of only one. Furthermore such brushes oifer greater resistance to the passage of current transversely through the brush from one segment to another, particularly when transformer voltages exist in the armature coils during their short-circuit at the brushes.

The object of the present invention is to provide a relatively simple means of controlling the distribution of the electrical loading of brushes of the spilt type aforesaid.

An electric current-collecting split brush according to the invention comprises a succession of two or more surface-sweeping parts which are not rigidly bonded together, to collect and transmit current in parallel paths between the surface of an electric commutator or slip-ring and a terminal connection and which may comprise a top metal plate to distribute the force of a pressure finger over the several surface-sweeping parts, and a cap element surmounting at least one of said parts and interposed in the path of current between said part and said terminal connection, said cap element underlying said top metal plate if such is comprised, the nature of said element and/or of its electrical contact with said part being such that a differential electrical eflect, including that due to contact resistance, is obtained, i.e. a different total electrical resisttance due at least in part to contact resistance in one of said parallel paths from that in another. By such means the distribution of current passing through respective parts of the brush may be varied as desired.

The invention is particularly advantageous in that it makes possible the use of surface-sweeping brush parts which have the same or substantially the same electrical properties whilst providing for a desired differential electrical efiect in the operation of the respective parts.

Nevertheless the invention is not necessarily limited to the surface-sweeping brush parts having substantially the same electrical properties, because it may be desired to have the respective parts of different composition or structure, and in this case the construction according to the invention will super-impose a differential effect to modify or add to that inherently due to the nature of the brush parts to produce the total differential eflEect that may be required.

A structurally common cap element may surmount all the brush parts, and may be a composite bridge piece composed of material of one electrical conductivity where it surmounts one brush part and of material of another electrical conductivity where it surmounts another brush part. In this case the cap element may be a continuum of varying composition, or may be of sandwich construction with the portions secured together with an intervening layer or layers of insulating material.

On the other hand there may be a separate cap element surmounting the respective parts of the brush. For example, in a two-part brush the cap element, on one part, may be of material having a comparatively high conductivity, e.g. comprising a mixture of 65% copper and 35% carbon, whilst the cap element on the other part may be of material having a comparatively low conductivity, e.g. carbon bonded with a resin. A cap element may be united with or attached to its associated brush part.

Each surface-sweeping brush part is not necessarily homogeneous. Thus in a two-part brush either or both parts may comprise two layers bonded together to form a sandwich, the junction surface of each sandwich being longitudinally of the brush. For example, an outer layer of a brush part may be made of more conductive material and have a substantially greater thickness, i.e. dimension transverse to the length of the brush, than the inner layer. In such cases contact between a cap element and one layer of the brush part it surmounts may be eliminated either by recessing or cutting away a part of the under side of the cap element or by reducing the length of a layer so that it does not extend into contact with the cap element. The layer thus kept out of contact with the cap element may be the inner or outer layer of the brush part concerned. Alternatively a cap element may be of sandwich construction similar to that of the brush part that it surmounts.

The invention in another of its aspects, employs a cap element formed integrally with a brush part, and surmounting but neither integrally formed with nor bonded to another brush part. Thus the brush comprises a cap element or bridge piece formed with one or more legs (i.e. brush parts) which extend to bear on the surface of the electric commutator or slip-ring. Alongside such leg or legs (i.e. brush parts) and capped by part of the bridge piece, there is or are located one or more other brush parts which bear on the collecting surface. The difierential effect is obtained, at least in part, by the fact that there is a contact resistance between the latter brush part (or parts) and the bridge piece, whereas the first brush part (or parts) is (or are) of course, integral with the bridge piece.

Accordingly for example a brush may comprise a member in the form of a T the leg of which extends to the collecting surface and is a brush part, and the top of which is a cap element, which, on each side of the leg, caps a brush part alongside the leg. Alternatively the brush comprises a member in the form of an inverted L so that there is a brush part in the recess which this form affords. The T form is particularly suitable for a reversible machine. The inverted L form is particularly suitable for a non-reversible machine, the leg of the L-member being generally the entering part in operation.

As indicated above, the amounts of current passing through the respective parts of the brush will depend not only on the conductivity of the brush materials in the respective paths between the surface of the electric commutator or slip-ring and the terminal connection, but also on the passage of current across the places of contact between the cap element (or cap elements) and the brush parts. Thus, alternatively or in addition to having a cap element, or two or more cap elements composed of materials of different conductivities, a differential electrical effect may be obtained by forming the surfaces where the cap element (or cap elements) and the underlying brush part (or parts) meet so as to produce any desired contact resistance.

If it is desired to increase the contact resistance in one or more surfaces where a cap element bears on a brush part, the area of contact may be reduced by appropriately shaping or cutting the cap element or brush part.

Brush devices according to the invention, i.e. the brush parts together with the cap element or cap elements, will normally be produced so that there will be less current through (i.e. the resistance will be higher in the path through) the part of the brush which in operation is the leaving part. In the case of reversible motors there will normally be at least three parts to the brush, the outside parts carrying less current than (i.e. the resistance in these paths will be higher than that through) the inside part (or parts).

The box in which the brush is accommodated may be made of insulating material or, if it is made of metal or other conductive material, at least one internal surface thereof may be provided with insulating material in order to prevent or reduce short-circuiting or current through the brush box from one part of the brush to another. For a similar reason a gap or insulation piece may be provided between the side faces of the cap element (or cap elements) and the interior surface of the brush box.

The brush parts may be made of any appropriate material, particularly carbon (including both natural graphite and electro-graphite), with or without the inclusion of metal which may in some cases be the predominating ingredient. It is a feature of the invention that appropriate material for the brush parts may be chosen in disregard of any desired differential action, as this can be obtained entirely by the provision of the cap element(s) according to the invention. This was not hitherto the case when such action was obtained solely by making the brush parts themselves of different composition, and when the best material to obtain the desired differential action often had unstable running properties, for example, high friction or inability to Withstand sparking. Materials which may be used for the composition of the cap element or cap elements are e.g. carbon, graphite and metal, which latter may be sintered. It will be appreciated that the electrical conductivities of the cap element (or cap elements) may be brought to predetermined values, for example by admixture of carbon or graphite with metal or with resistance material, or by infiltration of metal into blocks of porous material.

The connection leading from the cap element (or cap elements) may be a flex or flexes secured to the cap element (or cap elements) and any brush part which is not surmounted by a cap element, or a finger or fingers bearing on it or them. In the case where there are two or more separate cap elements surmounting their respective brush parts, each cap element, and any brush parts which are not surmounted by cap elements, may have a separate connection, e.g. .a spring finger bearing on the top of the member, and/or a flex, and the respective fingers or flexes will, in operation, be joined together at a common terminal. Indeed these connections may be different and supplement the differential effect already in the parallel paths.

In the case where a spring pressure contact finger bears on more than one top of a cap element and/or a brush part which is not surmounted by a cap element, it may sometimes be desirable to provide a top metal plate which surmounts at least two of these cap elements and/or brush parts, and on which the spring finger bears. Otherwise the spring finger may have an insufficient contact area to spread over all the cap elements and/or brush parts. Such a metal plate may have a side piece to be secured to the side Wall of one of the outer brush parts, or of a surmounting cap element, so as to permit independent freedom of movement to the respective parts of the brush together with any cap elements secured to them. In such a case the metal plate may have a different contact resistance with the brush part or cap element to which it is secured, from that with the other parts and/ or cap elements, but such different contact resistance is variable and not dependable. Such a top metal plate is not a cap element according to the invention. The differential effect according to the invention may be increased by attaching a flexible lead only to the brush part(s) or cap element(s) to which the metal plate is secured, thus lowering the resistance in the path(s) through this (or these) brush part(s). At the same time or alternatively the resistance in the path(s) that include(s) the brush part(s) and/or cap element(s) to which the metal plate is not secured may be rendered lower by connecting a flexible lead to this (or these) brush parts or cap element(s).

A cap element, or more than one cap element, and the underlying brush part(s) may be formed of an interlocked structure, so that on withdrawing one member, e.g. a cap element, from the surface of the commutator or slip-ring, one or more other members are also Withdrawn. In this case a cap element and an underlying brush part are mechanically connected by a claw arrangement of dove-tailed cross-section. According to the present invention a cap element may surmount more than one brush part, so that the cap element may be mechanically connected to any, some or all of the underlying brush parts. On the other hand a brush part may be formed so as to interlock with another brush part, e.g. in the case Where one or more of the brush parts extend the whole length of the brush, the latter part may be formed so as to interlock with the shorter brush part. Thus the longer brush may be formed with a step on its inner surface, and the shorter brush part with an overhanging abutment, so that on withdrawing the longer brush part the step locks with the overhanging abutment and so the shorter brush part, with its surmounting cap element, is withdrawn together with the longer brush part. A space should be left between the step and the overhanging portion so as to allow relative movement of the unbonded parts during operation. This is an example of an unbonded brush of unitary construction such that all the parts can be withdrawn together. Equally a cap element may be formed so as to interlock with a brush part or another cap element in a similar manner.

In the case where there is a metal plate having a side piece riveted to a brush part or cap element, the rivet may be extended so as to stand proud of the (or an) inner surface of the brush part or cap element through which it passes, and to fit into a recess on the (or an) inner surface of the adjacent brush part. On withdrawing the brush part or cap element to which the rivet is secured, the other brush part is also withdrawn. In such a case, the recess into which the proud end of the rivet fits should be large enough to avoid contact with this end of the rivet except when the brush is withdrawn, so as to avoid electrical contact between these parts, and/or it may be advisable to coat the rivet and/or brush part, with an insulating varnish.

The invent on will be more particularly described with reference to the accompanying drawings, in which:

Figure l is an elevational view of a split electrical} current collecting brush embodying the invention in one form in' which two brush parts are of similar or the Same material and two cap elements are of different materials, the two cap elements being pressed respectively by separate spring fingers;

Figure 2 is an elevational view showing a brush similar to that shown in Figure l, but modified to the extent that the cap elements are bonded together and are pressed 'by a single spring finger;

Figure 3 is an elevational view of a brush device similar'to that shown in Figure 2, but in which two cap elements are united to an intervening layer of insulating material;

Figure 4 is an elevational view of a brush including two parts having inclined top surfaces surmounted by cap elements having correspondingly inclined bottom surfaces, the adjoining portions of the cap elements adjacent to the brush parts being recessed;

Figure 5 is an elevational view of a modification of the brush shown in Figure 4, the Figure 5 construction including generally two brush parts each of which comprises two layers bonded together;

Figure 6 is an elevational view of a modified brush construction including a Tvshaped brush part with its stern between two other brush parts and with its top serving as a cap element;

Figure 7 is an elevational view of a further modification in which an inverted L-shaped brush part has its upper portion sewing as a cap element for an adjoining brush part;

Figure 8 is an elevational view of a brush similar to that shown in Figure 7, but including two brush parts underlying the upper portion of an inverted L-shaped brush part;

Figures 9 and 9 are vertical sections, on planes perpendicular to each other, of a modified brush assembly including brush parts of different lengths, a cap element surmounting the shorter brush part and a metallic retaining plate;

Figures 10 and 10 are respectively a vertcal section and a top plan view of a further form of brush assembly including three brush parts, cap elements and a metal plate;

Figure 11 is an elevational view of a further modification comprising a longer and a shorter brush part with stepped adjoining faces and a cap element surmounting the shorter brush part;

Figure 12 is an elevatonal view of a further form of assembly in which adjoining faces of two brush parts are stepped, the larger brush part having a piece surmounting the shorter brush part to serve as a cap element;

Figures 13 and 13 are respectively elevational views at ninety degrees to each other and showing a further form of brush including larger and shorter brush parts and a. separate cap element surmounting the shorter part; and

Figures 1.4 and 14* are respectively elevational views at ninety degrees to each other of a brush assembly including a shorter brush part and a cap element recessed at the surface thereof which engages the shorter brush part.

Figure 1 shows a tandem brush sweeping a surface 1 of an electric commutator or slip-ring. The brush cornprises parts 11 and 12 respectively surmounted by cap elements 21 and 22, to which are attached flexible leads 31 and 32. The cap elements may be separate from or mechanically connected to their underlying brush parts. Spring fingers 3 and 4 bear on the top of cap elements 21 and 22, respectively, to maintain the brush parts 11 and 12, respectively, in contact with the surface 1. Parallel paths of current run from the surface 1. One is through brush part 11, cap element 21 and flexible lead 31,- and the otheris through brush part 12, cap element 22 and flexible lead 32, to a common terminal 2. The brush parts 11 and 12 are composed of the same material, but cap elements 21 and 22 are composed of different materials. The differential effect is obtained by virtue of the different resistances of the materials of the cap elements 21 and 22 and of the different resistances made by their contact with the brush parts.

Figure 2 shows a split brush sweeping a surface 1 of an electric commutator or slip-ring, and comprising brush parts 11 and 12, which are respectively surmounted by cap elements 21 and 22 each composed of different materials. The cap elements are bonded together and pressed upon by a single spring finger 3. Flexible leads 31 and 32 are attached to cap elements 21 and 22 respectively. As in the preceding embodiment, the parallel paths are between the surface 1 and a common terminal (not shown), and the differential effect is obtained by virtue of the different resistances of the materials in the cap elements 21 and 22. In practice it is preferred to have some mechanical connection (not shown) between the cap elements and the brush parts, so as to facilitate withdrawal of the brush parts.

Figure 3 shows a split brush sweeping a surface 1 of an electric commutator or slip-ring, and comprising brush parts 11 and 12, and cap elements which are united to form a composite body of sandwich form, comprising outer elements 21 and 22, composed of different materials, and an inner layer of insulating material to reduce short circuiting. As in Figure 2 there is a single spring finger 3 and flexible leads 31 and 32 connected to cap elements 21 and 22, respectively.

Figure 4 shows a brush sweeping a surface 1 of an electric commutator or slip-ring, and comprising two brush parts 11 and 12, respectively surmounted by two cap elements 21 and 22, composed of materials of different conductivity, which are bonded together and recessed where their adjoining surfaces would otherwise meet the adjoining surfaces of brush parts 11 and 12. Alternatively, the brush parts, 11 and 12, may be recessed, instead of the cap elements, 21 and 22. A spring finger 3 bears on the top of the cap elements 21 and 22. The differential effect is obtained by virtue of the difference in conductivity of the cap elements.

Figure 5 shows a brush sweeping a surface 1 of an electric commutator or slip-ring and comprising two cap elements 21 and 22, which are composed of different materials, and which are bonded together and respectively surmount split brush parts each of which consists of two layers. Thus there are in all 4 brush part layers, namely the outer layers 11 and 12, and inner layers 14 and 15. Layers 11 and 14 are bonded together and are surmounted by cap element 21, while layers 12 and 15 are bonded together and are surmounted by cap element 22. Flexibles 31 and 32 are attached to cap elements 21 and 22 respectively, and to a common terminal 2. A spring finger 3 bears on the top of the cap elements. The cap elements are recessed so that they contact only outer layers 11 and 12, not the inner layers 14 and 15. The differential effect is obtained by virtue of the different resistances between the cap elements 21 and 22. In addition, more current passes through brush parts 11 and 12, than through brush parts 14 and 15, since the latter parts are not in direct electrical contact with the cap elements. Preferably there is some form of mechanical connection (not shown) between the cap elements and the brush parts, eg a mechanical claw or books.

Figure 6 shows another brush embodiment sweeping a surface 1 of an electric commutator or slip-ring, and containing a member 25 in the form of a T. The stem of the T is a brush part, while the top of the T is a cap element and surmounts, on either side of the stem, brush parts 11 and 12. A spring finger 3 bears on the top of the member 25. The differential effect is obtained by virtue of the contact resistance between the brush part 11 and the over-hanging part of the member 25 (and 7 similarly between the brush part 12 and the member 25) in the case where the brush parts 11 and 12 and the T-member 25 are all of the same material. As before it is preferred to have some form of mechanical connection (not shown) between the cap elements and the brush parts.

Figure 7 shows a brush sweeping a surface 1 of an electric commutator or slip-ring, and comprising an L-shaped member 27 and a brush part 12 in the recess formed by the L-member. The differential effect is obtained by virtue of the contact resistance between the brush part 12 and the L-member 27.

. Figure 8 shows a brush sweeping a surface 1 of an electric commutator or slip-ring, and comprising an L- shaped member 27, and brush parts 12 and 13 in the recess formed by the L-member. The differential effect is obtained by virtue of the contact resistances between the L-member 27 and the brush parts 12 and 13.

Figures 9 and 9 show a brush sweeping a surface 1 of an electric commutator or slip-ring and comprising a, relatively short brush part 11 surmounted by a cap element 21, and a relatively long brush part 12, a metal plate 28 surmounting cap element 21 and brush part 12 and having a side piece which is secured to brush part 12 by a rivet 7, and a flexible 32 is attached to the top of brush part 12. Figure 9 is a section taken on the line 9 9 in Figure 9. Rivet 7 stands proud of the inner surface of brush part 12, and fits into a larger recess in the inner surface of brush part 11, as shown in the figure. Thus on withdrawing brush part 12 by the flexible 32, brush part 11 and cap element 21 are also withdrawn. Cap element 21 can be readily exchanged and replaced by a cap element of a different material so as to alter the differential effect. If desired, cap element 21 may be recessed as shown at 25 in Figure 9 so as to localise the contact area between cap element 21 and brush part 11.

Figures and 10 show a brush sweeping a surface 1 of an electric commutator or slip-ring, and comprising brush parts 11 and 12 each surmounted by cap elements 21 and 22 and a brush part 13 positioned between brush parts 11 and 12. A metal plate 28 surmounts cap elements 21 and 22 and brush part 13, and has a dependent portion secured to the surfaces of brush part 13 which is adjacent to cap element 22 and brush part 12 by a rivet 7, which at either end stands proud of brush part 13 and fits into recesses in brush parts 11 and 12. A flexible lead 33 is attached to brush part 13. Figure 10 shows in plan view the relationship between flexible 33, metal plate 28, cap elements 21 and 22 and brush part 13. On withdrawing brush part 13 by the flexible 33, brush parts 11 and 12 and their surmounting cap elements 21 and 22 are also withdrawn. The ends of rivet 7 may be varnished to reduce the possibility of current flowing into the brush part 13 through the rivet 7. If desired of course, flexibles may be attached to cap elements 21 and 22, but the construction shown above enables the brush to be withdrawn merely by pulling on the flexible 33.

Figure 11 shows a brush sweeping a surface 1 of an electric commutator or slip-ring, and comprising brush parts 11 and 12, the latter being surmounted by a cap element 22, a flexible lead 31 attached to brush part 11 and spring fingers 3 and 4 bearing on brush part 11 and cap element 22, respectively. Brush part 11 is formed with a step X on its inner surface, and brush part 12 with an overhanging abutment Y, so that on withdrawing brush part 11 (by flexible 31) brush part 12 and its surmounting cap element 22 are also withdrawn. There is a space Z between the step X and the overhanging abutment Y to allow relative movement of the unbonded parts during operation. The differential effect is obtained by reason of the contact resistance between brush part 12 and cap element 22, and the difference in composition, if. ny, in the materials used.

Figure 12 shows a brush sweeping'asurface-1 ofan.

electric commutator or slip-ring, comprising brush parts 11 and 12. Brush part 11 is formed with a piece surmounting brush part 12, and with a step X which can engage with an overhanging abutment Y on brush part 12, as shown, there being a space Z between the step X and the abutment Y. As in the embodiment shown in Figure 10, when brush part 11 is withdrawn from the surface 1, brush part 12 will also be withdrawn. A flexible lead 31 is connected to and a spring finger 3 bears on the top of brush part 11. The differential effect is obtained by reason of the contact resistance between the top of brush part 12 and the overhanging part of brush part 11.

Figure 13 shows a brush sweeping a surface 1 of an electric commutator or slip-ring, and comprising brush parts 11 and 12, the latter surmounted by a cap element 22. Flexible leads 31 and 32 are connected to, and spring fingers 3 and 4 bear on the tops of brush part 11' and cap element 22 respectively. Cap element 22 is formed with a mechanical claw of dove-tailed cross-section, which interlocks with a groove in brush part 12, so. that on withdrawing cap element 22, brush part 12 is also withdrawn. The cross-section of the mechanical claw is clearly shown in Figure 13 which is a side elevation as viewed in the direction of the arrow A in Figure 13.

Figures l4 and 14 show a brush sweeping a surface 1 of an electric commutator or slip-ring, and comprising brush parts 11 and 12, cap element 22 surmounting and not bonded to brush part 12, flexible leads 31 and 32 connected to brush part 11 and cap element 22 respectively, and a spring finger 3 bearing on the top of brush part 11 and cap element 22. Cap element 22 is recessed as shown in the figures, so that the contact area between itself and brush part 12 is reduced. Thus the differential effect is varied by (a) changing this contact area, and (b) changing the pressure exerted by the cap element 22 on the brush part 12, while maintaining the same spring finger force.

What is claimed is:

1. A split electric current-collecting brush comprising a succession of at least two surface-sweeping parts which are capable of independent movement, to transmit current in parallel paths between a surface swept thereby and a terminal connection, and at least two cap elements each surmounting a surface-sweeping part and respectively interposed in the path of current between its respective surface-sweeping part and said terminal connection, said cap elements being composed of materials of different electrical conductivity, whereby there is produced an electrical resistance, including contact resistance between said cap elements and said surface-sweeping parts, in one of the said paths which is different from that in another of the said paths.

2. A split electric current-collecting brush comprising a succession of at least two surface-sweeping parts which are capable of independent movement, to transmit current in parallel paths between a surface swept thereby and a terminal connection, and at least two cap elements each surmounting a surface-sweeping part and respectively interposed in the path of current between its respective surface-sweeping part and said terminal connection, said cap elements being composed of materials of different electrical conductivity, and being combined together to form a unitary bridge piece, whereby there is produced an electrical resistance, including contact resistance between said cap elements and said surface-sweeping parts, in one of the said paths which is different from that in another of the said paths.

3. A split electric current-collecting brush comprising a succession of at least .two surface-sweeping parts of substantially the same composition, said surface-sweeping parts being capable of independent movement, to transmit current in parallel paths between a surface swept thereby and a terminal connection, and at least two cap elements each su'rrnounting a surface-sweeping part and respectively interposed in the" path of current between its respectivesurface-sweeping part and said' terminal connection, said cap elements being composed of materials of different electrical conductivity,.whereby there is produced an electrical. resistance, including contact resistance between said cap elements and said surface-sweeping parts, in one of the said paths which is different from that in another of the said paths.

4-. A split electric current-collecting brush comprising a succession ofat least two surface-sweeping parts which are capable of independent movement, to transmit current in parallel paths between a surface swept thereby and a terminal connection, andat least two cap elements each surmounting a surface-sweeping part and respectively interposed in the path of current between its respective surface-sweeping part and said terminal connection, said cap elements being composed of materials of different electrical conductivity, at least one of said surface-sweeping parts and the cap element surmounting the same being formed to be in contact over only part of their opposing surfaces, whereby there is produced an electrical resistance, including contact resistance between said gap elements and said surface-sweeping parts, in one of the said paths which is different from that in another of the said paths.

5. A split electric current-collecting brush, comprising a succession of at least two surface-sweeping parts which are capable of independent movement, to transmit current in parallel paths between a surface swept thereby and a terminal connection, at least one of said surfacesweeping parts being a longer surface-sweeping part, and at least one other of said surface-sweeping parts being a shorter surface-sweeping part, and at least one cap element, said cap element surmounting and being in electrical contact resistance contact with said shorter surfacesweeping part and being interposed in the path of current between said shorter surface-sweeping part and said terminal connection, such that there are different electrical resistances in the respective paths, due at least in part to the contact resistance between said cap element and said shorter surface-sweeping part.

6. A split electric current-collecting brush, comprising a succession of at least two surface-sweeping parts of substantially the same composition, said surface-sweeping parts being capable of independent movement, to transmit current in parallel paths between a surface swept thereby and a terminal connection, at least one of said surface-sweeping parts being a longer surface-sweeping part, and at least one other of said surface-sweeping parts being a shorter surface-sweeping part, and at least one cap element, said cap element surmounting and being in electrical contact resistance contact with said shorter surface-sweeping part and being interposed in the path of current between said shorter surface-sweeping part and said terminal connection, such that there are different electrical resistances in the respective paths, due at least in part to the contact resistance between said cap element and said shorter surface-sweeping part.

7. A split electric current-collecting brush, comprising a succession of at least two surface-sweeping parts which are capable of independent movement, to transmit current in parallel paths between a surface swept thereby and a terminal connection, at least one of said surfacesweeping parts being a longer surface-sweeping part, and at least one other of said surface-sweeping parts being a shorter surface-sweeping part, and at least one cap element, said cap element surmounting and being in electrical contact resistance contact with said shorter surfacesweeping part and being interposed in the path of current between said shorter surface-sweeping part and said terminal connection, and having a composition different from that of at least one of the said surface-sweeping parts, such that there are different electrical resistances in the respective paths, due at least in part to the contact I0 resistance between said cap element and said shorter surface-sweeping part.

8. A split electric current-collecting brush, comprising a succession of at least two surface-sweeping parts which are capable of independent movement, to transmit current in parallel paths between a surface swept thereby and a terminal connection, at least one of said surfacesweeping parts being a longer surface-sweeping part, and at least one other of said surface-sweeping parts being a shorter surface-sweeping part, and at least one cap element, said cap element surmounting said shorter surfacesweeping part and being interposed in the path of current between said shorter surface-sweeping part and said terminal connection, such that there are different electrical resistances in the respective paths, due at least in part to the contact resistance between said cap element and said shorter surface-sweeping part, and wherein the said longer surface-sweeping part is formed with a lateral step, and the said shorter surface-sweeping part is formed with an over-hanging abutment.

9. A split electric current-collecting brush, comprising a succession of at least two surface-sweeping parts which are capable of independent movement, to transmit current in parallel paths between a surface swept thereby and a terminal connection, at least one of said surface-sweeping parts being a longer surface-sweeping part, and at least one other of said surface-sweeping parts being a shorter surface-sweeping part, and at least one cap element, said cap element being formed by lateral ly extending said longer surface-sweeping part so as to surmount and be in electrical contact resistance contact with said shorter surface-sweeping part and be interposed in the path of current between said shorter surface-sweeping part and said terminal connection, such that there are different electrical resistances in the respective paths, due at least in part to the contact resistance between said cap element and said shorter surface-sweeping part.

10. A split electric current-collecting brush, comprising a succession of at least two surface-sweeping parts of substantially the same composition, said surface sweeping parts being capable of independent movement, to transmit current in parallel paths between a surface swept thereby and a terminal connection, at least one of said surface-sweeping parts being a longer surface-sweeping pan, and at least one other of said surface-sweeping parts being a shorter surface-sweeping part, and at least one cap element, said cap element being formed by lateral- 1y extending said longer surface-sweeping part so as to surmount and be in electrical contact resistance contact with said shorter surface-sweeping part and be interposed in the path of current between said shorter surfacesweeping part and said terminal connection, such that there are different electrical resistances in the respective paths, due at least in part to the contact resistance between said cap element and said shorter surface-sweeping part.

11. A split electric current-collecting brush, comprising a succession of at least two surface-sweeping parts which are capable of independent movement, to transmit current in parallel paths between a surface swept thereby and a terminal connection, at least one of said surfacesweeping parts being a longer surface-sweeping part, and at least one other of said surface-sweeping parts being a shorter surface-sweeping part, and at least one cap element, said cap element being formed by laterally extending said longer surface-sweeping part so as to surmount said shorter surface-sweeping part and be interposed in the path of current between said shorter surfacesweeping part and said terminal connection, such that there are different electrical resistances in the respective paths, due at least in part to the contact resistance between said cap element and said shorter surface-sweeping part, and wherein said longer surface-sweeping part is formed with a lateral step, and said shorter surfacesweeping part is formed with an over-hanging abutment,

11 y 12. A -split electric current-collecting brush, comprisev ing a succession of at least three surface-sweeping parts which are capable of independent movement, to transmit current in parallel paths between a surface swept thereby and a terminal connection, one of said surface-sweeping parts being a longer surface-sweeping part, and at least two of said surface-sweeping parts being shorter surface-sweeping parts, at least one of said shorter surface-sweeping parts being positioned on each side of said longer surface-sweeping part, and at least two cap elements, each cap element being formed by laterally extending said longer surface-sweeping part so as to surmount and be in electrical contact resistance contact with one of the said shorter surface-sweeping parts and be interposed in the path of current between said one of said shorter surface-sweeping parts and said terminal connectian, such that there are different electrical. resistances in the respective paths, due at least in part to the contact resistances between said cap elements and said shorter surface-sweeping parts.

References Cited in the file of this patent FOREIGN PATENTS 63,963 g (1st. add. of Pat. 2,020,066) 

